There has been known a care index called Braden scale for predicting a risk of pressure ulcer. This scale is based on the examinations and assessments of patient's physical conditions, including his sensation of pressure, wetness of skin, activeness, mobility, nutrient condition, and friction and shear occurring on his skin. The Braden scale is used to prognosticate pressure ulcers. By improving risky conditions and providing preventive measures against those factors that lead to pressure ulcer, it is possible to minimize development of pressure ulcers. Of the factors mentioned above, “friction” implies friction of an object slipping on skin by a relatively weak external. Friction is a risk factor in that it can damage the skin and become a cause of pressure ulcer. “Shear” implies compression or stretching of tissues lying between the skin and a bone occurring under a tangential stress due to a relatively strong external force acting on the skin. “Shear” is a risk factor in that it can cause blood stream inhibition leading to pressure ulcer.
As shown in FIG. 9, when the body of a patient 2 lying on a medical bed or nursing care bed, such as Gatch bed 1 whose back and knee sections can be bent (lifted), shearing forces “a” act on the patient's body in the direction from the lower half to the upper half of the body and shearing forces “b” act in the opposite direction. Such forces are generated over such regions of the patient's body as the scapula 3, lumbar 4, sacrum bone 5, and thighbones 6 during lifting up of the Gatch bed by a care worker in lifting and/or adjusting the patient's back and/or knee or moving the patient. When the patient 2 is too weak to move his body for himself, he cannot relieve himself of the shearing forces “a” and “b”. If the patient were left under such condition, the shearing forces would develop pressure ulcers at bony prominences.
Unfortunately, there is no known apparatus for measuring such shearing force actually acting on the patient's skin and causing pressure ulcer. As a consequence, no satisfactory analysis of shear has been made so far. Moreover, how a shearing force acts on the patient's body depends on the patient 2. That is, it depends on the region of the body the force acts, his weight and somato type, and whether a bony prominence exists or not. Thus, these factors must be also taken into account in the analyses. Therefore, in order to make more accurate the assessment of such care index as Braden scale, a need exists for an improved apparatus capable of accurately measuring a shearing force acting on patient's body.
In view of the circumstances as mentioned above, the invention is directed to an apparatus for accurately measuring the shearing force and pressure acting on the patient's skin and calculating the resultant force arising from the shearing force and the pressure accurately to evaluate risk factors that may cause pressure ulcer.